It's a 2003 harley fxdl. I've followed what looks like the power wire for the regulator and instead of hooking up to the battery it goes behind a silver box on the left side of the bike. How do I get to it? The box has 4 allen screws on the front side but I've turned and turned and they won't come out.

The regulator wire goes back to a breaker in that electrical caddy. If you can solder you can splice that wire anywhere. Do not just use a crimped on splice. That cover just pulls straight out. The bolts only hold the mounting pins that push into rubber grommets.